Stabilizing glycols



eeeeaeea May it, tees raise Edgar C. Brltton and Arthur It. Sexton, Midland,

Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Dela- This invention relates to stabilizing lower alkylene glycols against thermal decomposition. In certain types of aircraft and automotive engines, the liquid coolant, instead of running at the conventional temperature of 100 C. or less, commonly circulates at 150 C. in a closed system, and may occasionally reach 200 C. or higher, perhaps for an extended period. The problem of selecting a coolant which will operate satisfactorily at these temperatures and yet will not freeze even at extreme winter temperatures is a diflicult one. Ethylene glycol, undiluted or together with a lesser proportion of water, is most frequently chosen as the coolant, but it has the undesirable property of decomposing slowly at the higher temperatures mentioned to form carbon and gummy tars, which ultimately foul the heat-transfer surfaces and throttle circulation.

2 In so far as is known, any of the wood oils derived from the distillation of hardwood, or the autocondensates produced by heating such oils,

' may be employed as stabilizers for glycols ac- In consequence, with ethylene glycol coolants,

periodic overhauling of the circulating system is necessary, sometimes at short intervals.

In an effort to provide a more satisfactory liquid coolant for operation at higher temperatures, it has now been found that the lower alkylene glycols, such as ethylene glycol, may be stabilized against thermal decomposition of the type mentioned by incorporating therein a small proportion of a wood oil derived from the distillation of hardwood or an autocondensate of such an oil. These substances almost completely restrain thermal decomposition of the glycols, both in the undiluted state and in mixtures thereof with the same or a lesser weight of water, at temperatures up to 200C, and very markedly retard decomposition even when the glycols are maintained liquid under pressure at temperatures as high as 300 C.

Glycol compositions stabilized in accordance with the invention not only are useful as coolants for internal combustion engines but are satisfactory as liquid heat-transfer agents in general at temperatures within the range mentioned.

' They are characterized by extremely low freezing points, good heat-transfer characteristics, and moderate viscosities, as well as thermal stability. The compositions may also be used as fluid pressureand power-transmitting media.

The lower alkylene glycols to which the invention is applicable contain from two through five carbon atoms per molecule. 01 these, ethylene glycol, and to a lesser extent industrial mixtures of propylene glycols and of butylene glycols, are of present commercial interest. Such glycols may be employed according to the invention in the undiluted state or mixed with an equal or lesser weight of water. With larger proportions of water the boiling points of the solutions are somewhat low for a high temperature fluid, and thermal decomposition is rarely a serious problem.

cording to the invention. Of these oils, the one known as washed allyl oil, and its autocondensate, are perhaps the most eflfective.

In the hardwood distillation industry, the pyroligneous liquor, after the removal of settled tars, is subjected to a rough distillation in which the overhead fraction is crude methanol containing the alcohol oils, and the residue is crude acetic acid together with the acid oils. A number of different alcohol oil fractions are separated from the crude methanol by rectification, and several other oils, generally termed light oils and heavy oils, are recovered from the crude acetic acid and from the settled tar. All these fractions; which are complex mixtures of organic compounds, are included within the term wood oils as generally used, and are available as articles of commerce. The details of producing these individual oils are well nQwn'in the art, and are discussed, for example, in U. S. Patents 1,975,091 and 2,223,299. All such oilsare useful as thermal stabilizers for glycols, with the alcohol oils being preferred.

In the rectification of crude methanol, as well as of the pyroligneous acid itself, after the commercial methyl acetone and methanol have been distilled, there is obtained a fraction boiling higher than these latter, but lower than acetic acid, the cut usually being made near C. This fraction, which is known as wood spirits residue (U. S. 2,176,055), is the source of the washed allyl oil which is a preferred stabilizer according to the invention. In separating the latter, the wood spirits residue is first mixed with a roughly equal volume of water to remove soluble materials, particularly allyl alcohol, leaving an insoluble portion known as raw allyl oil. This raw oil is then mixed with aqueous sodium hydroxide in a quantity sufllcient to neutralize any acids and to saponify esters present, the mixture being heated slightly until reaction ceases. The remaining oily layer, which consists, at least in part, of water-insoluble unsaturated alcohols together with aldehydes and ketones, boils over the range.

of approximately to 0., and is known as washed allyl oil. If desired, it may be steamdistilled to separate it from traces of highboiling tars.

While the wood oils are themselves efiective stabilizers for glycols, they may, if desired, be subjected to autocondensation to produce higher boiling mixtures which are at least equally effective. To this end, a given'wood oil, e. g., washed allyl oil, may be heated at an elevated temperature, usually at least 200 C., in a closed vessel, either without or with a condensing catalyst such as sulfuric acid, until reaction ceases.

The resulting autocondensate is then used directly, or purified by steam-distillation.

In preparing thermally stabilized glycol compositions according to the invention, the wood oil polished testspecimens of aluminum, iron, brass, and copper were placed in the heated chamber throughout each run. The purposes of the metal specimens were to have present in the system l Discontinued becausejoi exoessiveldeoomposition.

or its autocondensate is simply-stirred into the 5 the metals normally used inliquid-cooled engines undiluted or aqueous glycol, in which it is soluble and also to observe the rates of corrosion of the to a limited extent. Alternatively, the wood oil metals.

stabilizer may be made up as a strong solution in In the examples, the washed allyl oil was oba mutual solvent, such as alcohol, and the solutained from hardwood distillation as described tion stirred into the glycol. Asmall proportion of above. The autocondensed washed allyl oil was the wood oil or autocondensate is all that is reproduced y eat ng Washed allyl 011 at 245 C.

quired to effect stabilization, 0.2 to 5 per cent by for 2 hours in a closed iron vessel.

weight of the glycol usually being satisfactory,

with 0.5 per cent or more being preferred. Example 1' Aqueu8 mixture at 200 The wood oils and their condensates, in addi- In each of the test runs summarized in the tion to preventing carbon and tar formation in Table, the system was filled with the given volume heated glycols and glycol-water mixtures, also of a mixture of 70 parts by weight of ethylene minimize corrosion of metals by these liquids beglycol and, parts of water, to which (except in cause of the fact that they almost completely the case of the blank) 0.5 part of the stabilizer restrain development of strongly acidic substances listed was added. The chamber was maintained by decomposition of the glycols. They also funcat 200 C. and circulation of the liquid was contin to a moderate degree as inhibitors in the continued for the period stated. The appearance of ventional sense of retarding the corrosion of the solution, the occurrence of aldehyde odor, metals by other agents, such as air, which may be and the presence of carbon and of tar in the dissolved in the glycol solution. However, when 25 chamber at the end of the test were noted. These extremely corrosive conditions are to be encoundetails are given in the Table. tered, it is preferable to rely on the wood oils as e eta test pecimens present in the chemthermal stabilizers only, and to introduce in addiher were weighed at the start of each run and tion a small proportion of a conventional corwere reweighed, af r ishin at the end of rosion inhibitor. Since many such inhibitors are so the run. Thelosses in wei t, fl ted as mi ithemselves unstable or volatile at temperatures of grams De h ur per q r n h of exposed sur- 200 to 300 0., it is important to select an inhibiface. are listed in the Table. tor which is not infected adversely by heating. r the results listed it will be seen that in Sodium silicate, usually from 0.5 to 5 per cent by the absence of a sta e aqueous ethylene glycol weight of the glycol, is a preferred choice. underwent considerable decomposition at 200 C.

While the heat-transfer media of the invention to form e ydes and carbon. Each of the staordinarily consist of the glycol and the stabilizer. bilizers ei e v p e e decomposition. a with or without water, minor proportions of other the solution and apparatus remained free of tar ingredients, such as anti-foaming agents, l akand carbon. The rates of corrosion of the metal stopping compounds, and dyes, as well as the con- Specimens w extremely w in all the r n xg ggggz 523122 already mentioned may be Emmple 2.-Undiluted glycol at 300 C.

The following examples will serve to illustrate Tests similar to those of Example 1 were carried the invention, but are not to be construed as out on undiluted ethylene glycol, using 0.5 per limiting its scope. In the examples, a testing cent of stabilizer. and maintaining the heated apparatus was employed consisting of an elecchamber at 800 C. The results are summarized trically heated closed iron chamber of about 400 in the Table. cc. capacity and a circulating system for with- From these tats, it is evident that the B137 drawing the liquid being tested from a reservoir, t c p ses ve rapidly at 800 C. The forcing it under a pressure of 100 to 120 pounds stabilizers entirely prevented formation of carbon per square inch into one end of the heated chamand tar, althoulh som aldehyde! were formedber, removing it from the other end of the chamve u der these e tre e Severe (lend-1011B, t her through a relief valve, cooling it, and-returnmar ed efleet ve eee 0f t e Sta e s, d t e ing it to the reservoir. The rate of circulation low rates of corrosion of the metal specim n are was controlled at about 800 cc. per hour. Weighed quite apparent.

Table Corrosion Rate, mgmJhn/sq. in. v Stablizer g s V0103? Appearance Aldehyde Tar Carbon Iron Brass Copper EXAMPLE 1.-7o PER CENT oLYooL AT 200' 0.

None washed 81m 011 i% 51% 5733mm".-. 3 Rte-.133: tti 31$ 33% 823i Agt ocondensed washed allyl 1,505 Clear brow-11.- do 4 0.1!) 0.02 0.02 0.01

EXAMPLE 'a-ioo ran CENT GLYCOL A'l sm- 0.

None 1 12.5 1, 020 Dark brown.-. Strong" Excessive.-. Excessive.-. (Excessive eerboniution dared t impomible.) Washed allyl oil 100 2,260 Clear gmennn Non Non 0.08 0.10 0.12 0.01 Agt ooondensed washed allyl 100 1,790 (In an rln (In 0,04 0,05 0,31 0,00

tially of a lower alkylene glycol containing from 2 through 5 carbon atoms per molecule and not over an equal proportion 'by weight of water stabilized against thermal decomposition by a small proportion of a substance selected from the class consisting of washed allyl oil and the autocondensate thereof in a proportion of from 0.2 to 5 percent by weight of the glycol.

2. A heat-transfer medium chemically stable at elevated temperatures consisting essentially of ethylene glycol and from about 0.2 to about 5 per cent by weight thereof of washed allyl oil.

3. A heat-transfer medium chemically stable at elevated temperatures consisting essentially of ethylene glycol and from about 0.2 to about 5 per cent by weight thereof of the autocondensate of washed allyl oil.

4. A liquid heat-transfer medium chemically stable at elevated temperatures consisting essentially of one part by weight of ethylene glycol. not over one part of water, and 0.005 to 0.05 part of washed allyl oil.

5. A liquid heat-transfer medium chemically stable at elevated temperatures consisting essentially of one part by weight of ethylene glycol. not over one part of water. and 0.005 to 0.05 part of the autocondensate of washed allyl oil.

6. In a process wherein a heat-transfer medium consisting essentially of a lower alkylene glycol containing from 2 through 5 carbon atoms per molecule and not over an equal proportion by weight of water is heated as a liquid for a prolonged period at an elevated temperature, the method of minimizing thermal decomposition of the liquid which comprises maintaining dissolved therein a small proportion of a substance selected from the class consisting of washed allyl oil and the autocondensate thereof in a proportion of from 0.2 to 5 percent by weight of the glycol.

7. In a process wherein ethylene glycol is heated as a liquid at an elevated temperature. the method of minimizing decomposition of the liquid which comprises maintaining dissolved therein from 0.2 to 5 per cent by weight of washed allyl oil derived from the distillation of as a liquid at an elevated temperature, the meth 0d of minimizing decomposition of the liquid :hich comprises maintaining dissolved therein from 0.2 to 5 per cent by weight of the autocondensate of washed allyl oil derived from the distillation of hardwood.

9. In a process wherein a liquid mixture of ethylene glycol and a lesser proportion of water is heated at an elevated temperature, the method of minimizing decomposition of the liquid which comprises maintaining dissolved therein washed allyl oil derived from the distillation of hardwood in a proportionof from 0.5 to 5 per cent by weight of the glycol.

1.0. In a process wherein a liquid mixture of ethylene glycol and a lesser proportion of water is heated at an elevated temperature, the method of minimizing decomposition of the liquid which comprises maintaining dissolved therein the autocondensate of washed allyl oil derived from the distillation of hardwood in a proportion of from 0.5 to 5 per cent by weight of the glycol.

- EDGAR 0. BRI'I'I'ON. ARTHUR R. SEXTON.

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS 2,223,299 Chesley NOV. 26, 1940 

